I'm trying to setup postfix to send mail on my machine (Ubuntu 10.04). It only needs to send mail and will be used by the php mail() function in a few scripts. I have a google apps account that will receive all the mail for the domain (and it is currently working with no problems).

I've just installed postfix, and am trying to follow the configuration for a 'null' server from the postfix web site. i.e. my main.cf file looks like this:

Also, I wasn't sure what to do when the instructions told me to change master.cf, so I haven't changed anything yet, but I don't think this should impact sending mail.
/etc/postfix/master.cf:
Comment out the local delivery agent entry

However I'm getting the following errors after trying to send an email to my personal account with the command:

On debian-based distributions like Ubuntu you can use dpkg-reconfigure postfix which will present a configuration dialog in your terminal. It's quite easy that way, but read the explanations carefully.